refactor(bridge): split fx bridge, stabilize VST3 host chain, drop old install engines

- remove diagnostic canaries from audio hot path (crackle fix) and
  stuck C5 note raw-MIDI test (Vst2Instrument::init noteOff)
- split native bridge into daw_vst_bridge (VSTi) + fx_vst_bridge (VST FX)
- VST3: processData prepare before setActive, zero input buses, accept
  both .vstpreset and bridge-state blob in RenderJob presets
- native_render/vst_engine: bridge-exe discovery + render_fx_chain + /fx-gui
- delete old install/ engine binaries (install via sidecar+resources now)
- add BUILD_LAYOUT.md, build_selfcheck, tools/ diagnostics

tools/scan_stack_refs.py

@@ -0,0 +1,54 @@
+import struct
+
+path = r"C:/Users/locpham/AppData/Local/Temp/sf_dumps/bridge_crash_1696.dmp"
+data = open(path, "rb").read()
+
+sig, ver, numstreams, sdir = struct.unpack_from("<IIIIIIQ", data, 0)[:4]
+streams = {}
+for i in range(numstreams):
+    stype, datasize, rva = struct.unpack_from("<III", data, sdir + i * 12)
+    streams[stype] = (rva, datasize)
+
+mods = []
+rva, sz = streams[4]
+n = struct.unpack_from("<I", data, rva)[0]
+pos = rva + 4
+for i in range(n):
+    base, imgsz, cksum, ts, name_rva = struct.unpack_from("<QIIII", data, pos)
+    nlen = struct.unpack_from("<I", data, name_rva)[0]
+    name = data[name_rva + 4:name_rva + 4 + nlen].decode("utf-16-le", "replace").rstrip("\x00")
+    mods.append((base, imgsz, name))
+    pos += 108
+
+def mod_for(addr):
+    for base, szz, name in mods:
+        if base <= addr < base + szz:
+            return base, name
+    return None, None
+
+# dump all memory regions, scan for qwords inside DUNE 3.dll or bridge exe
+targets = []
+for base, szz, name in mods:
+    if "DUNE" in name or "daw_vst_bridge" in name:
+        targets.append((base, szz, name))
+
+print("targets:", [(hex(b), s, n.split("\\")[-1]) for b, s, n in targets])
+
+rva, sz = streams[5]
+n = struct.unpack_from("<I", data, rva)[0]
+pos = rva + 4
+hits = {}
+for i in range(n):
+    start, msz, mrva = struct.unpack_from("<QII", data, pos)
+    pos += 16
+    chunk = data[mrva:mrva + msz]
+    for j in range(0, len(chunk) - 8, 8):
+        val = struct.unpack_from("<Q", chunk, j)[0]
+        for tb, tsz, tn in targets:
+            if tb <= val < tb + tsz:
+                hits.setdefault((val, tn, val - tb), []).append((start + j, msz))
+                break
+
+print("\nunique qwords pointing into DUNE/bridge (addr, module, offset, count):")
+for (val, tn, off), locs in sorted(hits.items()):
+    print("  %016x %s+%x  (seen %d times, e.g. mem@%016x size %x)" % (val, tn.split("\\")[-1], off, len(locs), locs[0][0], locs[0][1]))